1. Field of the Invention
The present invention relates to a sheet-metal centrifugal pump casing, and more particularly to a sheet-metal centrifugal pump casing which is capable of inhibiting deformation at the liner portion thereof, for example, even when an external force acts upon the suction flange.
2. Prior Art
In general, centrifugal pump casings made of sheet metals are known in which a casing shell having a suction port is formed from a stainless steel plate through a deep drawing process using a press and a suction flange is firmly attached to the suction port on the casing shell.
Centrifugal pump casings of this type tend to be lacking in strength because they are made of sheet metals, and, when the pump casing, for example, is subjected to an operating pressure, or internal pressure, i.e., the total pressure occurring as a result of centrifugal force of the impeller and the suction pressure acting on the suction side, or when the suction flange is acted upon by an external force due to piping, there is the possibility that these internal pressures and external forces will be transmitted to the pump casing and cause deformation of the liner portion thereof. When the liner portion is deformed, a contact spot occurs thereon with the impeller which causes problems such as noise and pump overload, and in extreme cases results in failure of the impeller due to contact between the casing shell and the impeller.
To prevent this, a configuration has been proposed such that, in addition to providing a portition body inside the casing shell which provides a partition between a suction chamber and a pressure chamber, a so-called flexible free structure is employed as part of said casing shell at the portion extending outwardly from such a partition body, whereby only a part of the casing shell is deformed because of such free structure when the external force due to piping as described above is applied so that such deformation does not reach the partition body.
Also, a configuration has been proposed such that a plurality of reinforcing members are securely extended between a suction flange and a casing shell to obtain a so-called rigid structure so that the external force due to piping acting upon the suction flange is directly transmitted to the casing shell where the external force due to piping may be absorbed by the casing shell itself.
However, there is a problem in the casing of the so-called flexible free structure that piping process becomes troublesome, because it is necessary to support the suction pipe with respect to the base structure by using another member while connecting the suction pipe to the suction flange.
Also, in the case of the so-called rigid structure, though no problems appear in normal use, deformation occurs at the liner portion of the casing shell leading to the problem of a contact spot as described above such as when the suction flange is subjected to an excessive external force which cannot be absorbed by the casing shell.